Swinefordite

Chemical formula: Ca<sub>0.2</sub>(Li,Al,Mg,Fe<sup>3+</sup>,Fe<sup>2+</sup>)<sub>3</sub>(Si,Al)<sub>4</sub>O<sub>10</sub>(OH,F)<sub>2</sub>·nH<sub>2</sub>O

Swinefordite is a very rare, soft mineral from the smectite group, forming microscopic, white or colorless flakes and aggregates.

## Characteristics Swinefordite is a hydrated lithium, calcium, magnesium, and iron aluminosilicate, belonging to the smectite group (montmorillonite subgroup). It occurs as extremely small, flexible, hexagonal plates and flakes, which typically form compact, earthy or chalk-like aggregates. Individual crystals are visible only under an electron microscope. Due to its fine-grained nature, it appears macroscopically as a soft, white or colorless mass. ## Physical Properties This mineral is very soft, with a Mohs hardness of just 1, meaning it can be scratched with a fingernail. It has a silky or dull luster and is translucent. The density of swinefordite is approximately 2.25 g/cm³. It exhibits perfect cleavage in one direction, which is typical for clay minerals. ## Colors and Varieties Swinefordite is usually colorless to white. No colored or commercial varieties have been distinguished. ## History and Name The mineral was first described in 1975 by Pei-lin Tien, Robert B. Rowe Jr., and James B. Goff. Its name honors Ada Swineford (1917-1993), an American geologist and mineralogist specializing in clay minerals, a professor at Western Washington University. ## Uses Swinefordite has no industrial or commercial significance. Its occurrence is solely of scientific and collecting value for specialized micromineral collectors.

Properties

Mohs hardness
1
Luster
Dull
Streak
White
Density
2.25
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Macroscopic identification of swinefordite is practically impossible without advanced analytical techniques. In a collection, it is identified based on the label from its primary locality. It is characterized by its white color, earthy or chalky texture, and extreme softness. It reacts with water by swelling. ## Distinguishing from Similar Minerals It can be confused with other white clay minerals, such as kaolinite, montmorillonite, or talc. It is distinguished from talc by its reaction with water (talc is hydrophobic). Definitive distinction from other smectites requires X-ray diffraction (XRD) and chemical analysis (EDS/WDS) to confirm the presence of lithium. ## Crystal Forms It forms microscopic, pseudohexagonal flakes and plates less than 2 micrometers in size. Aggregates appear as compact, earthy or chalk-like masses.

Geological environment

## Genesis Swinefordite is a secondary mineral, formed as a result of hydrothermal alteration of lithium-rich rocks. It forms in alteration zones of lithium pegmatites, where it replaces primary lithium minerals such as spodumene or petalite. ## Mineral Associations It most commonly co-occurs with quartz, microcline, albite, muscovite, spodumene, bikitaite, and cookeite. ## Localities The most important and classic localities for this mineral are: - Type locality: Tanco pegmatite in Bernic Lake, Manitoba, Canada. - Foote Lithium Co. Mine, Kings Mountain district, Cleveland County, North Carolina, USA. - Bikita, Masvingo Province, Zimbabwe.

Rarity

Very rare

For collectors

## Quality Criteria The quality of swinefordite specimens is assessed primarily based on the richness and purity of aggregates on the rock matrix. As it is a micromineral, specimens are typically small. The most desirable samples are those from a well-documented, classic locality, co-occurring with other rare lithium minerals. ## Popular Localities The most prized specimens by collectors come from the Foote mine in North Carolina (USA) and the Tanco pegmatite in Canada.

Care and storage

## Cleaning Swinefordite specimens are extremely delicate and sensitive to water. They should not be washed in water or other liquids, as, being a clay mineral, it can swell and disintegrate. The safest method for removing dust is to use a soft brush or carefully blow off particles. ## What to Avoid Contact with water and chemicals must be strictly avoided. The mineral is very soft, susceptible to scratches and mechanical damage. It should be protected from moisture, high temperatures, and direct sunlight. ## Storage It is recommended to store specimens in sealed, stable "micromount" containers, which protect against dust, moisture, and physical damage. Avoid storing in areas with fluctuating air humidity.

Sources

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